The invention relates to the general field of thin film microcircuits with particular reference to conductive leads for attachment to GMR (giant magneto-resistive) sensor elements.
FIG. 1 is a schematic illustration of the read portion of a read-write head used in magnetic recording. The principal elements are a strip of magneto-resistive material 11, contact to which is made through leads 12. Sensor strip 11 is located between magnetic shields 13 and 14 (14 also serves as one of the pole pieces of the write head; it is shown as partly stripped away for purposes of clarification). The space between these various elements is filled with an insulating material, such as aluminum oxide (not shown).
Information, stored as stripes of magnetized material, is contained in storage layer 15 which moves below the sensor in a direction 16. The principle governing the operation of read sensor 11 is the change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance). The magneto-resistance effect manifests itself as an increase in resistivity when the material is magnetized in a direction perpendicular to the easy axis, said increase being reduced to zero when magnetization is along the easy axis.
It is now known that the magneto-resistance effect can be significantly increased by means of a thin film structure known as a spin valve. The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
At the present time, leads (such as 12 in the figure) are formed from laminates of tantalum/gold/tantalum. This combination has proven satisfactory as it is relatively low resistance (due to the gold) and has high corrosion resistance. It is, however, anticipated that newer GMR sensors such as HPD (High Performance Drive) and HDR(High Data Rate) will require leads that, in addition to possessing the above properties, are also harder and have a higher melting point. These additional properties are needed because of harsher environments (e.g. higher RPM) that these newer sensors will encounter.
A routine search of the prior art did not turn up any references that describe the exact structure of the present invention. The search did, however, uncover several references that were of interest. For example, U.S. Pat. No. 5,883,764(Pinarbasi) shows conductive leads comprised of Ta, Cr, and Ta. U.S. Pat. No. 5,268,806(Goubau et al.) shows a conductive lead comprised of Ta. U.S. Pat. No. 5,491,600(Chen et al.) teaches a multi-layered lead comprised of Ta and Au while U.S. Pat. No. 5,742,459(Shen et al.) also discloses a multi-layered lead structure.
It has been an object of the present invention to provide a conductor lead for a magneto-resistive sensing element in a magnetic recording system.
Another object of the invention has been that said lead be compatible with HDP and HDR type GMR heads.
A further object of the invention has been that said lead have low sheet resistance, high corrosion resistance, high melting point, and a high hardness value.
These objects have been achieved by providing a lead structure comprising a layer of ruthenium or rhodium sandwiched between layers a nickel-chromium alloy. The lower nickel-chromium layer acts as a seed that ensures that the ruthenium and rhodium over-layers have crystal structures that have low resistivity. The interfaces between these three layers introduce a minimum of interfacial scattering of the conduction electrons keeping dimensional increases in resistivity to a minimum.